The March CPS includes a supplement weight which allows the records to sum to the total non-institutionalized population. Each person is assigned a weight based on person characteristics (such as race, etc) such that the records sum to the total population in accordance with the Bureau’s projections of Decennial Census population levels.
The first adjustment made to the time series was to allow for a consistent weight basis for the time series. When the March 2002 file was released, the weights were benchmarked to the 2000 Census. Previously, the years from 1990 forward had been benchmarked to the 1990 Census. Census then released sets of 2000 consistent weights for both March 2000 and March 2001. Moving to 2000 weights more accurately reflects the underlying population, but causes some discontinuity in the time series in the first year the new weights are used. To correct for this, we determined the total change in population due to the shift to 2000 consistent weights and then WORKING PAPER, 31 MARCH 2005 Page 15 of 34 spread the increase smoothly back across 10 years. Specifically, we calculated the percentage increase in the population for CY 2000 and 2001 by race and by age and then averaged the percentage increase across the two years for each cell. This increase was then spread across ten years (the full decade) with CY 2000 having the full increase and CY 1991 having a factor of 1.00 (unchanged). These factors were used to increase the person weights, record by record, on the CPS files from March 1995 through March 1999.
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